The research program will examine the selective processing of semantic information. A series of dual channel discrimination tasks have been proposed, in which words will be defined as relevant or irrelevant on the basis of one dimension, and may be identified as targets within the attended class of stimuli on the basis of a second attribute. Event- related brain potentials (ERPs) will be recorded in order to determine the circumstances under, and extent to which, words classified as irrelevant are semantically processed. The use of ERPs will also permit quantification of the chronometry of the two decisions when these are based on physical or semantic characteristics of the stimuli. A further intent of this research will be to better define the psychological functions associated with, and brain areas subserving certain ERP components which are thought to reflect the selection of relevant stimuli for additional processing.